Lost circulation is a phenomenon that various working fluids leak into the formation under pressure difference in various downhole operation processes, including well drilling, well cementation and completion, testing, well reparation, etc. Shale gas is stored in mud shale. Shale formations have developed micro-cracks and pores, most of which are at micro-nano level. In a drilling process, the filtrate of drilling fluid invades into the micro-cracks in mud shale first, the micro-fractures extend and expand quickly under a hydration effect, and develop along the fractures, eventually resulting in damaged mud shale and lost circulation. At present, common plugging agents such as calcium carbonate, asphalt, resin, film former, etc. are difficult to enter into the fractures owing to their large particle size and shape mismatch with the fractures, resulting in an unsatisfactory plugging effect. Owing to the advantages of small particle size, high dispersity and good stability, nano-materials can effectively enter into micro-nano-scale fractures and pores for effective plugging, form a dense plugging layer to prevent further invasion of the liquid phase and thereby attain the purpose of plugging. However, conventional nano-plugging materials are rare. In addition, with conventional nano-plugging materials, an agglomeration phenomenon may easily occur owing to the small particle size and high surface activity. As a result, the particle size is increased, and an expected plugging effect can't be achieved.
Therefore, there is an urgent need for an innovative micro-nano plugging agent in the art to solve the problem of lost circulation in shale formations.